1. Field of the Invention
The present invention relates to a collision detecting system for detecting a collision with a pedestrian at a front portion of a vehicle.
2. Description of the Related Art
It has been demanded to protect not only a driver and passengers of a vehicle but also a pedestrian on a road.
In an occupant protection system of a vehicle to meet such a demand, various protection devices for relieving shocks that are caused when a pedestrian collide with a portion of the hood of a vehicle have been proposed. In such a protection system, it is important to provide a collision detecting system for detecting a collision of a vehicle with a pedestrian.
For example, a wire, a strain gauge, an optical fiber, etc. are installed into the front bumper of a vehicle to form a collision detecting system, which detects a collision based on the tension of the wire, the output signal of the optical fiber and the attenuation of light that passes through the optical fiber. However, in order to form such a collision detecting system at a front portion of the vehicle, it is necessary to provide an installation space inside the bumper, which necessitates a substantial work time to install.
Another collision detecting system that utilizes a bumper reinforcement member, side members and a crush box, which are existent members of the vehicle, has been proposed. As shown in FIGS. 18 and 19, this collision detecting system includes a strain gauge 4 and a strain inducing member 5 that is distorted according to a strain caused by the side member and the crush box 3 when a portion of the bumper collides with an object. If a strain is generated in the crush box 3, the strain is transmitted to the strain inducing member 50, whose strain is detected by the strain gauge 4.
Normally, the strain inducing member 50 has a flat portion, and a pair of stay portions 52, which are fixed at a preset distance from each other to the crush box 3 by bolts or the like. When a stress is applied to the crush box 3 in a direction such that the preset distance is reduced, the flat portion swells, as shown in FIG. 18 or dents as shown in FIG. 19. The strain gauge 4 generates a positive output signal when the flat portion swells, while the strain gauge 4 generates a negative output signal when the flat portion dents. Therefore, it is difficult to accurately detect what kind of object the vehicle collide with or how sever the collision is.